A Study of the Efficacy of Troxerutin in Preventing Thrombotic Events in COVID-19 Patients

The goal of this clinical trial is to learn if troxerutin works to prevent thrombotic events in mild or severe COVID-19 patients. It will also learn about the safety of troxerutin. The main questions it aims to answer are: * Does troxerutin lower the number of thrombotic events in participants? * What medical problems do participants have when taking troxerutin? Researchers will compare troxerutin to a placebo (a look-alike substance that contains no drug) to see if troxerutin works to prevent thrombotic events in COVID-19 patients. Participants will: * Take troxerutin or a placebo every day for 7 days. * Visit the clinic at the first, fourth, seventh and 28th days after enrollment for checkups and tests * Keep a diary of their symptoms and the number of times of thrombotic events, bleeding events and type II HIT-related thrombocytopenia